Abstract: The super hybrid rice “Liangyoupeijiu” was used as the test material in comparison with “Shanyou 63” and “9311”. The comparison studied the changes in the activities of key enzymes involved in nitrogen metabolism, included NR (nitrate reductase), GS (glutamine synthetase), GPT (glutamic-pyruvie transaminase), GOT (glutamic-oxalacetic transaminase), GDH (glutamate dehydrogenase) and protease, in rice flag-leaves at the late developmental stage. The kinetics of NR, GS and GPT, contents of soluble proteins and free amino acids, and panicle traits were also investigated at the same time. The study was to build better understanding into the changes in the activities and dynamics of enzymes related with nitrogen metabolism in super hybrid rice, its parents and control variety at the late developmental stage. The study further explored the inherent mechanisms of these changes and provided scientific basis for regulating nitrogen metabolism in hybrid rice at the late developmental stage. The results showed that one week after blooming was the high-value duration of the activities of enzymes related with nitrogen metabolism in flag-leaves of the three rice varieties. After one week, the enzymes activities entered into the sharp-fall phase. The NR, GS, GPT and GDH activities and speaks activities among the varieties were significantly different. One week after blooming, higher activities of GS and GDH in “Liangyoupeijiu” rice variety were noted. Then 7~14 days after blooming, NR and GS activities in “Shanyou 63” rice were significantly higher than those of “9311” and “Liangyoupeijiu”. Also GS and GDH activities and peak activities in “Shanyou 63” were higher and occurred at much later dates than those in the other two varieties at late grain-filling stage. At flowering and initial grain-filling stages, “9311” had higher trans-aminase and catalytic activities with nitrogen metabolism starting earlier than in the other varieties. The changes in GDH and GOT activities at late developmental stage suggested that oxidative deamination was the main vivo process. The relation between activities and catalytic activity of NR and GS were nonlinear at late developmental stage. Catalytic activity of GPT was lowest at 14 days after anthesis. As three kinds of enzymes at the late grain-filling stage still had higher catalytic activity combined with changes in soluble proteins and ATPase activity in flag-leaves, it was proposed that the contents of protein enzymes were the main factors affecting enzyme activity and nitrogen metabolism at the late developmental stage. The energy state of flag-leaves was an important limiting factor to the availability of physiological activity. The inter-specific hybrid rice (“Shanyou 63”) had the advantage of high physiological activity in the leaf and grain-filling stages than the sub-specific hybrid rice (“Liangyoupeijiu”). This was the main sources of changes in key enzyme activities, grain-filling rates and panicle traits.